This invention relates to building technology, and in particular to wire lath which may be used to reinforce coatings, such as stucco, applied to soffits and other building surfaces.
Some building construction techniques involve the application of a coating, such as stucco, to a surface. The coating may be desired, for example, to improve appearance, enhance fire resistance or to comply with building or fire codes. In the following disclosure the term xe2x80x9cstuccoxe2x80x9d is used generally to apply to cementitious plasters or gypsum plasters, including stuccos as defined in applicable building codes.
When applying a coating of stucco (or other similar material) it is generally desirable to provide a lath on the surface. The lath provides reinforcing for the stucco and holds the stucco in place while it cures. Difficulties can be encountered in applying stucco to overhanging surfaces such as soffits (i.e. the area under building eaves) and the undersides of exposed roof areas, such as porticos. In such areas gravity tends to cause the stucco to sag after it has been applied.
The framing for soffits is typically open. Framing members typically extend transversely across the soffit opening at regular spacings (for example, 16 inches or 24 inches center-to-center). A lath is applied across the opening and attached to the framing members. Stucco is then applied to the lath. The lath supports the stucco and, after the stucco dries, reinforces the stucco. Stucco may be applied in various ways including by hand trowel, or by spraying onto the lath. In either case significant pressures can be imposed on the lath.
The lath must meet several requirements. First, it must be rigid enough to withstand the stresses of the stucco being applied. If the lath is deflected significantly during installation, then stucco in areas adjacent to the deflected area will be disturbed and will likely fall out. Second, the lath must provide adequate reinforcement so that the stucco coating on the soffit will be able to withstand maximum expected wind pressures. The lath should have features which provide good keying and embedment of the stucco over the entire area of the lath. Third, the lath should be designed in such a way as to assist in making the layer of stucco even in thickness. A stucco layer which is uneven in thickness can be prone to cracking.
In many applications it is desirable to have a backing membrane integrated with the lath. A backing membrane prevents stucco from blowing through the lath. Such a membrane is especially desirable in applications where stucco will be pumped or sprayed onto the lath.
Various types of lath have been developed for soffit applications. Specialty expanded metal laths are very widely used. Such laths have been produced by companies such as Alabama Metal Industries Corporation of Birmingham, Ala. under the trade-mark AMIC(trademark). AMICO""s expanded metal lath products currently include:
xe2x85x9xe2x80x3 Rib Lath (xe2x80x9cFlat Ribxe2x80x9d). This lath has eighteen ribs approximately xe2x85x9 inch high, spaced 1xc2xd inches on center to provide rigidity for horizontal applications. The lath has a large number of openings or xe2x80x9ckeysxe2x80x9d which provide keying for either troweled or machine-applied stucco.
xe2x85x9cxe2x80x3 Rib Lath (xe2x80x9cHigh Ribxe2x80x9d). This lath has seven longitudinal ribs, each xe2x85x9c inch deep and eight small flat ribs to provide additional rigidity for horizontal applications. A herringbone mesh is located between the ribs to provide keys for good bonding of the stucco to the lath.
Cal Spray Rib (xe2x80x9cxe2x85x9 Inch Flat Ribxe2x80x9d). This is a more rigid lath which includes strips of kraft paper attached between the ribs. The added rigidity makes this product well suited for horizontal applications, such as soffits. The paper helps reduce the amount of plaster waste and is not intended to be moisture resistant. A version of Cal Spray Rib having xe2x85x9c inch high ribs is also available. Similar products have been available from California Expanded Metals Company (CEMCO(trademark)) and others.
Expanded metal lath products such as those described above can provide good rigidity and stiffness for their rated spans. They also provide good keying and hang on surfaces. However, these products have some disadvantages. First, at the locations of the stiffening ribs, the stucco is much thinner than it is at other locations. Furthermore, the ribs present unbroken surfaces which do not provide opportunity for embedment and keying of stucco. This typically results in a series of cracks forming along each of the ribs.
Another disadvantage of prior expanded metal lath systems is that the keys are typically quite small. Correct installation practice requires the edges of adjacent sheets of lath to be overlapped. However, with small key openings it is typically impossible to force stucco adequately through the lath in the overlapping portions. This results in a weak zone in which the stucco is likely to crack at each point where sheets of the lath overlap.
A third difficulty with expanded metal lath is that it is difficult to cut, especially if the ribs are high. When cut, expanded metal lath typically exhibits razor sharp edges. This makes current expanded metal lath products tedious and even dangerous to install.
Another group of stucco laths sometimes used for soffits are wire fabric laths. Wire fabric laths typically comprise a rectangular mesh of wires which are welded at their intersections. Wire fabric laths have been available, for example, from the Georgetown Wire Company, Inc, of Fontana, Calif. under the trademark K-LATH(trademark). Some examples of such laths include:
Stucco-Rite(trademark) standard. This product is a self-furring sheet of galvanized welded-wire-fabric lath, 16 gauge by 16 gauge, with 2 inch by 2 inch openings. A perforated absorbent carrier kraft paper is incorporated into the mesh, and a Grade D water proofed breather building paper is laminated to the back side of the kraft paper. A heavy duty version features an 11 gauge stiffener wire every 6 inches.
Standard xe2x80x9cGun Lathxe2x80x9d. This is a flat sheet welded wire lath, with 2 inch by 2 inch openings, 16 gauge by 16 gauge with a 13 gauge stiffener wire every 4 inches along length of the sheet. An absorbent, slot perforated kraft paper sheet is incorporated between the face and back wires. A heavy duty version features an 11 gauge stiffener wire every 6 inches on center.
xe2x80x9cSoffit Lathxe2x80x9d. This product is similar to Gun Lath with 16 gauge by 16 gauge wires, but with grid spacing at 1.5 inches by 2 inches. The backing kraft paper has smaller perforated openings which are to provide a more positive keying for the soffit stucco.
Wire fabric laths are more worker friendly than the expanded metal laths in that they are easy to cut, and do not present as many sharp edges when cut. They are also easy to overlap without blinding the openings at the overlap areas. This reduces cracking at overlaps of sheets. Further, there are no stiffening ribs that can cause cracking. Therefore, the overall finished stucco is much better since cracking is minimized.
However, current paper-backed wire laths have two major disadvantages. First, the relatively large wire grid spacing provides little hang on surface area for the wet stucco to hang onto. The perforated backing kraft papers do prevent blow through, but do not have sufficient keying or suction capability to hang onto the wet stucco.
A second disadvantage of current wire lath products is that they are not as rigid as is desirable. These laths tend to deflect as the plasterer applies force. After the force is removed the lath springs back. As this happens fresh plaster in adjoining areas can be dislodged and fall out. This exacerbates the stucco fall out problem. Therefore, plasterers must apply stucco to wire lath very carefully. This is a major disadvantage since it slows down speed of application. Even so, there is typically a high wastage of stucco.
Rigidity can be increased somewhat by using larger diameter wires. However, increase in wire diameter does very little to increase stiffness. If wire diameters are increased enough to provide significant increases in rigidity then the large wires close to the stucco surface tend to cause the stucco to crack along the large wires.
A third disadvantage of some current paper backed wire laths is that the installed stucco plaster has uneven thickness which results in additional cracking of the stucco. This problem is exacerbated because the paper is tightly attached to the wire lath itself. This prevents the stucco from totally surrounding the wires of the lath. As a result the attachment of the stucco to the lath is weaker than would be desired and the stucco can separate from the lath under certain loading conditions.
Jaenson, U.S. Pat. No. 5,540,023 discloses an improved wire lath in which a layer of backing paper is held in place between two courses of horizontal wires. The backing paper is not tightly attached to the lath and allows good keying. However, this wire lath requires that the welds of the lath be made through perforated holes in the backing paper. The backing paper must have a hole at each intersection between two wires. This is a disadvantage for producing laths with smaller grid spacings, since the amount of hole area required becomes very large, leaving less and less paper area. This is a major disadvantage for soffit applications since increasing the hole area results in increased blow-through. Further the kraft paper could easily tear between holes resulting in even more blow-through.
Japanese patent application No. 06047691 published on Sep. 9, 1995 (JP 07233611A2) discloses a multi-layer spray wall core body having a porous sheet between sheets of erected reinforcements. Japanese patent application No. 09347789 published on Jul. 6, 1999 (JP11181989A2) discloses another paper-backed wire lath.
Despite the wide variety of lathing systems that are currently available there remains a need for a lath which avoids the disadvantages discussed above.
This invention provides a wire lath that can be made to be more rigid than current wire lath products and overcomes a number of disadvantages of expanded metal laths.
Accordingly, one aspect of the invention provides a welded wire lath comprising a plurality of generally parallel transverse wires lying primarily in a first plane. The transverse wires each depart from the first plane in a plurality of spaced-apart bent sections. Each bent section is defined between first and second shoulder portions. While the bent sections can have various shapes, a V-shape is preferred. The bent sections preferably have widths not greater than their heights. The lath also comprises a plurality of generally parallel first longitudinal wires. The first longitudinal wires lie generally in the first plane. They intersect with and are attached, preferably by welding, to the transverse wires. The first longitudinal wires include, for each of the plurality of bent sections, a longitudinal wire attached to each of the transverse wires in at least one of the shoulder portions corresponding to the bent section. The lath also comprises a plurality of generally parallel second longitudinal wires. The second longitudinal wires lie generally in a second plane parallel to and spaced apart from the first plane. The second longitudinal wires are attached to the bent sections of the transverse wires. The second longitudinal wires in conjunction with the bent sections and those first longitudinal wires which are attached at the shoulders of the bent sections form trusses which provide rigidity to the wire lath. The trusses may also serve as furring spacers although separate furring spacers may be provided.
In preferred embodiments of the invention the first longitudinal wires include, for each of the plurality of bent sections, a pair of longitudinal wires. One of the pair of longitudinal wires is attached to each of the transverse wires in a first one of the shoulder portions. The other one of the pair of longitudinal wires is attached to each of the transverse wires in the second one of the shoulder portions.
The wire lath may incorporate a barrier layer disposed between the first and second planes. In preferred embodiments the barrier layer is perforated by elongated transversely-extending apertures and the bent sections pass through the apertures. The barrier layer may comprise a suitable building paper, such as kraft paper, which may be surface treated to improve the adhesion of stucco. The barrier layer may have additional perforations which do not coincide with intersections of the longitudinal wires and transverse wires. The additional perforations serve as xe2x80x9ckeysxe2x80x9d for stucco.
A backing layer, such as a layer of asphalt-coated paper may be adhesively affixed to the barrier layer. In this case the second longitudinal wires extend between the backing layer and the barrier layer.
The wires of a wire lath according to the invention do not need to be round. In some embodiments at least some of the first longitudinal wires are non-round in cross section. The non-round longitudinal wires may advantageously be flattened and oriented to lie generally in the first plane. This provides increased surface area for stucco adhesion, and also can facilitate the application of stucco.
Further features, aspects and advantages of the present invention will be more fully understood when considered with respect to the following detailed description, appended claims, and accompanying drawings.